The strength of weak ties
The strength of weak ties is a seminal paper in the study of social networks and a hugely famous paper in sociology more generally. The paper raises the argument that the study of social networks can be a tool for studying sociology more generally, raises a hypothesis about the usefulness of certain types (i.e., weak) ties in certain situations, and uses empirical data from a study on job search to show the value of weak ties in this case.
Granovetter defines a tie (and its strength) as, "a combination of the amount of time, the emotional intensity, the intimacy (mutual confiding), and the reciprocal services which characterize the tie." The paper suggests that there is a "forbidden triad" which says that if AB and connected, and A and C are connected, B and C will also be connected. This is particularly the case if the ties are strong between two people.
Granovetter argues that some ties can act as a "bridge" (referencing a brokerage positions) that spans parts of a social network and connected otherwise disconnected social groups but argues strongly that "no strong tie is a bridge." The argument is that if someone is strong tied to someone else, those around their tie will also be tied to them and ties will be redundant. Granovetter argues that for diffusion across a network, is the weak ties that are most valuable. He argues that diffusion studies tend to not be sociometric and those that are do not characterize the tie type.
Granovetter used empirical evidence from a survey of job seekers. He asked people who had found a job through contacts how often they saw the person that had helped them with their job. 56% saw their contacts only occasionally and 28% saw them rarely skewing strongly toward the "weak" end of the spectrum. Nearly half of these job contacts were made with only one network hop implying a very close network.
Another important, but less emphasized, aspects of Granovetter's work is the strong emphasis on linking macro and micro theories. Weak ties, Granovetter argues, are more likely to link different groups together and so can provide a way of connecting the literatures on small groups or families with more macro discussions of social structure. The paper argues that personal experience is largely connected up with large-scale aspects of social structurally.
Theoretical and practical relevance:
Granovetter's article is one of the most influential articles in all of social science has been cited more than 20,000 times. It is perhaps the seminar article in contemporary social network analysis.